Ask any New York head-hunter and they will tell you the talent has moved uptown. At the other end of Manhattan, far removed from the investment banks of Wall Street or the media conglomerates of mid-town, the bright young things are heading straight to Harlem to get a foot in the door at the Clinton Global Initiative.

Alongside the Bill and Melinda Gates Foundation or Google.org, CGI stands at the forefront of the latest trend in wealthy giving: philanthrocapitalism. A fashionable form of high-value charity that has now crossed the Atlantic and started to catch on among London's more socially minded plutocrats. Indeed, with the appointment of the multimillionaire philanthropist Jennifer Moses as special adviser to the prime minister, the approach has made its way into the highest reaches of government. Yet, as a timely pamphlet by philanthropy guru Michael Edwards warns, the grandiose claims of philanthrocapitalism can both overplay its results and mask its more nefarious effects.

Despite all the claims of modernity, "venture philanthropy" often looks a great deal like old-fashioned giving. America basked in Mark Twain's Gilded Age 100 years ago, flaunting the same extraordinary concentrations of wealth and poverty that are so evident today. Then, the riches of the Mellons, Carnegies and Rockefellers came from steel, oil, and natural resources, rather than the IT and finance boom of the 1990s.

Yet the urge to give something back remains. And one cannot but be impressed that over the next 40 years, $55 trillion in philanthropic resources are expected to be created in the US alone. These modern robber barons could have simply spent their gains on ever more sumptuous ranches, islands or wives, but choose instead to deploy it fighting TB or funding inner-city literacy pushes. But their way of doing so, Edwards suggests, is not always in the best interests of civil society.

Philanthrocapitalism is a transposition of the corporate model into the charitable sector. Having made their fortunes in the market, new philanthropists see no reason why the same tight, business strictures cannot simply be applied to the non-profit domain. Instead of bureaucratic government initiatives or the cosy, self-satisfied ethos of established charities, philanthrocapitalists like Bill Clinton want to "repurpose business methods and business culture to solve the world's problems". This means, in the words of one philanthropic consultancy, "an entrepreneurial results-oriented framework, leverage, personal engagement and impatience". Indeed, the entire vocabulary of Silicon Valley is applied to social rather than corporate enterprise.

Of course, in our media culture of Dragon's Den and The Apprentice, commerce can do no wrong. But Edwards suggests that the bottom-line ethos of the business world is not necessarily in accordance with the demands of accountability, voice, and an engaged public sphere that effective charity requires. Civil society needs just the kind of inefficiencies - multiple, overlapping organisations; willingness to debate; steady accumulation of experience; a public space that unites ethnicities and classes - that hedgefunders find abhorrent. Moreover, the philanthrocapitalist system is often based on an ideal of passive consumption rather than intimate engagement by donor and recipient, while the power to dictate public policy deployed by the likes of Clinton, Warren Buffet or eBay founder Jeff Skoll can often seem positively undemocratic.

And this is the point: the philanthrocapitalists pride themselves as consciously post-political. "The venture-capital ethos means instead that these social entrepreneurs are almost willfully blind to ideological issues," David Brooks of the New York Times wrote admiringly before describing a dinner with Bill Gates. "He looked utterly bored as the conversation drifted to presidential campaign gossip. But when asked about which programmes produce higher reading scores, the guy lit up and became a fountain of facts and findings."

There is little engagement with the kind of structural injustices - racial, economic, social - or broader environmental, demographic or strategic challenges that require political advocacy. Having made their riches from the existing free-market model, venture philanthropists see little need to confront its problematic aspects. And, given their accelerating influence in media and government, such an approach closes down a broader ideological debate. But Edwards argues that we shouldn't be constrained by these limited horizons. "Over the last century, far more has been achieved by governments committed to equality and justice, and social movements strong enough to force change through, and the same might well be true in the future. No great social cause was mobilised through the market in the 20th century."

In one sense, of course, all this is a very American debate. The problem in the UK is sadly not yet a surfeit of giving. It is a super-rich who have yet to realise their social, ethical or cultural responsibilities. But with Moses settling into No 10, an ever more hubristic City and a wider disbelief in the capacity of government, despite all of Edwards's objections the philanthrocapitalist model looks eerily on the march.